When a damper disc is used for an automobile clutch disc, it is preferable to prevent three kinds of vibrations such as the idle rattle, the driving rattle and the low frequency abnormal vibration (tip-in and tip-out). In a conventional clutch disc, however, it has been difficult to prevent these three kinds of vibrations simultaneously.
For example, the applicant of the present invention has conventionally developed a clutch disc (Japanese Published Patent Application No. 61-40847), in which a disc-like hub flange of a spline hub has been divided into an inner peripheral part and an outer peripheral part, a weak torsion spring has been installed in the inner peripheral part, strong torsion springs have been installed in the outer peripheral part, so that the weak spring is made to function for a small torsion angle range and the strong springs are made to function for a large torsion angle range. However, this prior art has been effective for the idle rattle and the driving rattle but ineffective for the low frequency abnormal vibration. Further, in a clutch disc (Japanese Patent Application No. 60-44300, Patent Publication No. 61-201933) wherein a first friction material provided with a high friction coefficient and a second friction material provided with a low friction coefficient have been installed to increase or decrease a hysteresis torque according to a torsion angle, it has been possible to prevent the driving rattle and the low frequency abnormal vibration but impossible to prevent the idle rattle.
Moreover, the applicant of the present invention has also developed a disc clutch (Japanese Patent Application No. 58-82319, Patent Publication No. 59-208226) wherein a key has been installed between an inner peripheral side flange and an outer peripheral side flange of said Published Patent Application No. 61-40847 so that the key can be freely connected or disconnected according to a torsion angle. However, a technical measure to utilize this disconnectable key for preventing the three kinds of vibrations has not been disclosed in this prior art.
An object of this invention is to provide a damper disc which can exert a low torsional rigidity in a small torsion angle and a large torsional rigidity in a large torsion angle, has a small hysteresis torque characteristic within a working range of fine angle and a large hysteresis torque characteristic within a working range of large angle, and can exert a large hysteresis torque characteristic for a high torsional angular velocity even within a fine working angle.